1,721,171 research outputs found
Covert communications with a full-duplex receiver in non-coherent Rayleigh fading
No full textIn a majority of research on covert communications, knowledge about channel state information (CSI) of main channel and/or warden channel is assumed to be known or partially known. However, a covert user may not afford to perform channel estimation in practice, and acquiring the warden's CSI is even impossible. In this paper, we investigate covert communications over non-coherent Rayleigh fading channels, in both i.i.d. fast fading and slow fading cases. We observe that the purpose of covert communication in many scenarios is to hide the existence of the sender, not the receiver. Therefore, we allow the receiver to work in full-duplex mode such that it can emit artificial noise (AN) while receiving signals simultaneously. We analyse the achievable covert rates with fixed and varying AN power and show that in both fast and slow fading cases, it is possible to achieve a positive covert rate. For the slow fading case, we further extend the proposed strategy to a multi-user scenario, in which multiple other users share the same spectral resource and cause interference at the warden. Extensive simulations are performed to verify the correctness of our analysis, which provide new insights on the AN design problem in non-coherent channels
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Lattice decoding for multi-input multi-output communications
No full textThis thesis is concerned with decoding for wireless communications. In particular, computationally efficient lattice decoding algorithms are exploited to further improve the system performance. Based on this idea, five technical chapters are presented in this thesis.
In Chapter 2, we propose novel lattice decoding based on segment Lenstra-Lenstra-Lovász (LLL) algorithm to further reduce the decoding complexity of coded Multiple-Input Multiple-Output (MIMO) cooperative channel. In particular, we extend the original segment LLL algorithm to the complex version, and prove that it can achieve the optimal diversity-multiplexing tradeoff (DMT).
In Chapter 3, we present randomized lattice decoding based on Klein's sampling technique, which is a randomized version of Babai's nearest plane algorithm (i.e., successive interference cancellation). We analyze and optimize the performance of randomized lattice decoding resulting in reduced decoding complexity, and propose a very efficient implementation of random rounding.
Chapter 4 is concerned with bounded distance decoding (BDD) based embedding technique. The embedding technique is used to reduce the γ-BDD problem to 1/(2γ)-unique shortest vector problem 1/(2γ)-uSVP). WE prove that the Lenstra, Lenstra and Lovász (LLL) algorithm can achieve 1/(2γ)-BDD for γ ≈ O(2n) for embedding decoding. We also prove that BDD of the regularized lattice is optimal in terms of the DMT.
In Chapter 5, we present a detailed study of the soft output MIMO decoding. We show that the randomized decoding algorithm is an efficient way to compute soft output. In order to improve soft output quality, we propose variants of soft output decoding based on the sampling technique and embedding technique. Moreover, we derive a lower bound on the search radius for which list-based decoding can provide a near optimal solution to soft output.
In Chapter 6, the performance limits of lattice reduction-aided precoding are investigated. The proximity factor is defined to measure the worst-case transmission power gap to sphere precoding. The second moment over precoding region is defined to measure the average-case transmission power loss. Afterward, low dimension lattice precoding is proposed to further reduce the transmission power
Distributed signal processing using nested lattice codes
Full text linkMulti-Terminal Source Coding (MTSC) addresses the problem of compressing correlated sources
without communication links among them. In this thesis, the constructive approach of this problem
is considered in an algebraic framework and a system design is provided that can be applicable
in a variety of settings. Wyner-Ziv problem is first investigated: coding of an independent and
identically distributed (i.i.d.) Gaussian source with side information available only at the decoder
in the form of a noisy version of the source to be encoded. Theoretical models are first established
and derived for calculating distortion-rate functions. Then a few novel practical code implementations are proposed by using the strategy of multi-dimensional nested lattice/trellis coding. By
investigating various lattices in the dimensions considered, analysis is given on how lattice properties affect performance. Also proposed are methods on choosing good sublattices in multiple
dimensions. By introducing scaling factors, the relationship between distortion and scaling factor
is examined for various rates. The best high-dimensional lattice using our scale-rotate method can
achieve a performance less than 1 dB at low rates from the Wyner-Ziv limit; and random nested
ensembles can achieve a 1.87 dB gap with the limit. Moreover, the code design is extended to
incorporate with distributed compressive sensing (DCS). Theoretical framework is proposed and
practical design using nested lattice/trellis is presented for various scenarios. By using nested
trellis, the simulation shows a 3.42 dB gap from our derived bound for the DCS plus Wyner-Ziv
framework
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